Hi, Guys

For exchange 2013/ exchange online, I know it is easier to have external scanner to scan inbound/outbound email , but i don't know if it is possible to have internal email was scanned by external MTA before deliver to internal recipients. anyone know how to  achieve this and if the MTA can change email content?

please advice urgent from where this can be done , thanks very much!!

• Moved by Jason Johnston [MSFT]Microsoft employee 21 hours 48 minutes ago Not a development question.

Hi Tony,

According to your description, I understand that you want to use MTA to scan internal message to ensure security.
If I misunderstand your concern, please do not hesitate to let me know.

Whats the meaning of MTA? Message Transfer Agent or the term "MTA" to mean what Exchange refers to as the "Transport? Transport service handle message routing, more details about Mail Flow, for your reference:
https://technet.microsoft.com/en-us/library/aa996349(v=exchg.150).aspx#TransportPipeline
The internal message never leave Exchange Organization, so external MTA cannot used for internal mail flow.

However, we can deploy anti-spam agent on Mailbox Server to improve security, for example Sender filter, Sender ID agent and content filter agent.
I find an article about Anti-spam protection, for your convenience:
https://technet.microsoft.com/en-us/library/jj218660(v=exchg.150).aspx#Mailbox

Best Regards,
Allen Wang